Hydraulic system for boom hoist cylinder crane

ABSTRACT

A crane having an upper works rotatably mounted on a lower works and a boom pivotally mounted on the upper works includes a hydraulic boom hoist cylinder and a hydraulic circuit for controlling the hydraulic boom hoist cylinder. The hydraulic cylinder is pivotally connected to a mast on the upper works and pendently connected to the boom. The boom hoist cylinder preferably comprises two double-acting hydraulic cylinders. The hydraulic circuit includes a closed loop pump and a hydraulic controller connecting the closed loop pump and the double-acting cylinders such that fluid from the pump can be directed either to extend or retract the cylinders, with the hydraulic fluid exiting the cylinders being directed to return to the pump.

REFERENCE TO EARLIER FILED APPLICATIONS

[0001] The present application is a continuation of application Ser. No.09/061,804 filed Apr. 16, 1998, which in turn claims the benefit under35 U.S.C. § 119(e) of the filing date of Provisional U.S. patentapplication Ser. No. 60/041,555 filed Apr. 16, 1997, which is herebyincorporated by reference. Other patent applications and U.S patentsreferred to herein are also hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to construction equipment, such ascranes. In particular, the present invention relates to a crane having ahydraulic circuit to control a hydraulic boom hoist cylinder. Aspects ofa crane incorporating the preferred embodiment of the invention aredisclosed in the following pending U.S. patent applications: patentapplication Ser. No. 08/834,673, filed Apr. 1, 1997; patent applicationSer. No. 08/834,724 filed Apr. 1, 1997; patent application Ser. No60/041,555, filed Apr. 16, 1997; patent application Ser. No. 08/845,843,filed Apr. 25, 1997; patent application Ser. No 08/826,627, filed Apr.3, 1997; patent application Ser. No. 08/842,974, filed Apr. 25, 1997;and patent application Ser. No. 08/950,870, filed Oct. 15, 1997; thedisclosures of which are hereby incorporated by reference.

[0003] Construction equipment, such as cranes or excavators, often mustbe moved from one job site to another. Moving a crane or an excavatorcan be a formidable task when the machine is large and heavy. Forexample, highway limits on vehicle-axle loads must. be observed andoverhead obstacles can dictate long, inconvenient routings to the jobsite.

[0004] One solution to improving the mobility of large constructionmachines, such as cranes, is to disassemble them into smaller, moreeasily handled components. The separate components can then betransported to the new job site where they are reassembled.

[0005] The typical practice has been to use an assist crane todisassemble the crane into the separate components. The assist crane isthen used to load the components onto their respective transporttrailers. Once at the new job site, another assist crane is used tounload the components and reassemble the crane. As the components for alarge crane can weigh as much as 80,000 lbs., the capacity of the assistcrane required represents a very significant transport expense.

[0006] As a result, designers have attempted to develop self-handlingsystems for assembling and disassembling cranes. The majority of theself-handling systems developed thus far have been directed to smallercranes which need to be disassembled into only a few components.

[0007] The development of self-handling systems for larger cranes,however, has met with limited success. One reason for this is thatlarger cranes need to be disassembled into numerous components, thusrequiring time-consuming disassembly and reassembly procedures. Forexample, a large capacity crane typically uses a complicated andcumbersome rigging system to control the angle of the boom. Boom riggingsystem components such as the equalizer, the backhitch, and wire roperigging are heavy and difficult to disassemble for transport. Anotherreason for the limited success of prior art self-assembling cranes isthat they typically rely on additional crane components that are usedonly for assembling and disassembling the crane. For example, someself-assembling cranes require additional wire rope guides and sheaveson the boom butt so that a load hoist line can be used with the boombutt to lift various crane components during the assembly process. Anexample of one prior art method for disassembling a typical largecapacity crane is disclosed in U.S. Pat. No. 5,484,069.

[0008] It is therefore desirable to provide a crane and method ofself-assembly which reduces the number of parts which must be deriggedand removed to disassemble the crane for transport. In addition, it isdesirable to eliminate components which are only used during the craneassembly process. A crane which uses one or more hydraulic cylinders asboom hoist cylinders to control the boom angle would thus beadvantageous.

[0009] Cranes and other equipment often use hydraulic actuators,primarily motors and cylinders, to power the components of the equipmentThe hydraulic power for such actuators is normally supplied by one ormore diesel engines powering one or more hydraulic pumps. The hydraulicsystems for cranes and other equipment have ordinarily been open loopsystems, where hydraulic fluid is drawn from a low pressure reservoir,such as an atmospheric pressure tank, into the intake of the pump. Fluidexpended by the actuators is returned to the reservoir. Closed loophydraulic systems are more energy efficient, but generally are morecomplicated. It would be advantageous if a closed loop hydraulic systemwould be used to operate the various components of the equipment,including the boom hoist cylinders.

[0010] Prior art hydraulic circuits are known for operatingdouble-acting hydraulic cylinders with a closed loop pump. For example,U.S. Pat. No. 3,425,574 to Willgrubs et al. discloses a power shovelwith a double-acting cylinder. Closed loop piston pumps are used topower the cylinder in both directions by changing the direction of themotor powering the pumps. The cylinder of Willgrubs has a ratio of thechange of volume of the rod end of the cylinder to the change in volumeof the piston end of the cylinder of about 1:2.78. The additional fluidneeded to compensate for this difference in volume is taken care of byfour vane pumps. However, because of the arrangement of the system, thevane pumps add fluid to the closed loop portion of the circuit bydischarging into the high pressure side of the circuit.

SUMMARY OF THE INVENTION

[0011] In preferred aspects, the invention provides a crane having oneor more hydraulic boom hoist cylinders and a hydraulic circuit tocontrol the hydraulic boom hoist cylinders.

[0012] In one aspect, the invention is a crane having an upper worksrotatably mounted on a lower works and a boom pivotally mounted on theupper works comprising a mast pivotally connected to the upper works; adouble-acting hydraulic cylinder having a bore, a piston mounted in thebore and forming a piston end of the cylinder, and a rod connected tothe piston opposite the piston end and extending out of an exit end ofthe bore but being seated at the exit end of the bore, thus forming arod end of the cylinder, the cylinder having a first passageway incommunication with the piston end and a second passageway incommunication with the rod end, one of the piston end of the cylinderand the rod being pivotally connected to the upper works and the otherof the piston end of the cylinder and the rod being pivotally connectedto the mast; a closed loop hydraulic pump having, during operation, alow pressure port in fluid communication with a low pressure side of thehydraulic circuit and a high pressure port in fluid communication with ahigh pressure side of the hydraulic circuit; and a directional flowcontroller and hydraulic lines connecting the closed loop pump and thedouble-acting cylinder such that fluid from the pump can be directed toeither the first or second passageways and fluid from the other of thefirst or second passageways is then directed to return to the pump.

[0013] In a second aspect, the invention is hydraulic circuit comprisinga first double-acting hydraulic cylinder having a bore, a piston mountedin the bore and forming a piston end of the cylinder, and a rodconnected to the piston opposite the piston end and extending out of anexit end of the bore but being sealed at the exit end of the bore, thusforming a rod end of the cylinder, the cylinder having a firstpassageway in communication with the piston end and a second passagewayin communication with the rod end; a closed loop hydraulic pump having,during operation, a low pressure port in fluid communication with a lowpressure side of the hydraulic circuit and a high pressure port in fluidcommunication with a high pressure side of the hydraulic circuit; adirectional flow controller and hydraulic lines connecting the closedloop pump and the double-acting cylinder such that fluid from the pumpcan be directed to either the first or second passageways and fluid fromthe other of the first or second passageways is directed to return tothe pump; a second hydraulic pump in fluid communication with the closedloop hydraulic pump so as to supply make-up hydraulic fluid to the lowpressure side of the hydraulic circuit when the rod is being extended;and a relief valve in fluid communication with the first passageway whenthe rod is being retracted to allow excess hydraulic fluid to flow outof the circuit.

[0014] In the present invention, the use of a hydraulic cylinderpivotally connected at one end to the upper works of a lift crane and atthe other end to the mast, and used to control the boom angle, is asignificant advantage over other commercial cranes in use today.Further, to be able to use a double-acting cylinder for the boom hoistfunction, and to be able to use a closed loop pump to power thecylinder, is a further unique feature of the crane The unique hydrauliccircuit of the present invention allows a double-acting hydrauliccylinder to be powered by a closed loop pump, with make-up fluid neededwhen the cylinder is being extended to be supplied by a second pumpfeeding the low pressure side of the closed loop pump.

[0015] These and other advantages, as well as the invention itself, willbecome apparent in the details of construction and operation as morefully described and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a right side elevational view of a complete boom hoistcylinder crane incorporating a hydraulic boom hoist cylinder and ahydraulic circuit to control the hydraulic boom hoist cylinder made inaccordance with the teachings of this invention.

[0017]FIG. 2 is a partial right side elevational view of the boom hoistcylinder crane showing some of the internal components of the craneupper works.

[0018] FIGS. 3-7 are right side elevational views of the crane insequential stages of lower works assembly.

[0019] FIGS. 8-10 are right side elevational views of the crane insequential stages of upper counter weight assembly.

[0020] FIGS. 11-12 are partial right side elevational views of the cranein sequential stages of the wire rope guide repositioning.

[0021] FIGS. 13-15 are right side elevational views of the crane insequential stages of boom top and boom insert assembly.

[0022]FIG. 16 is a partial right side elevational view of the crane witha boom parking device engaged.

[0023] FIGS. 17-20 are partial right side elevational views of the cranein sequential stages of the repositioning of an alternative embodiment awire rope guide.

[0024]FIG. 21 is a schematic of the hydraulic circuit which controls thehydraulic boom hoist cylinders.

DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS OF THEINVENTIONS

[0025] While the present invention will find application in all types ofcranes or construction machines, the preferred embodiment of theinvention is described in conjunction with the boom hoist cylindercrawler crane 10 of FIGS. 1 and 2. The boom hoist cylinder crawler crane10 includes an upper works 12 having a rotating bed 14 which isrotatably connected to a lower works 16 by a swing bearing 18. The lowerworks 16 includes a car body 20, car body counter weights 22, and twoindependently powered crawlers 24.

[0026] The upper works includes a boom 26 pivotally connected to theupper works 12. The boom 26 comprises a boom top 28 and a tapered boombutt 30. The boom 26 may also include one or more boom inserts 32connected between the boom top 28 and the boom butt 30 to increase theoverall length of the boom 26. The angle of the boom 26 is controlled bya pair of hydraulic boom hoist cylinders 34 pivotally connected to theupper works 12. A mast 36 is pivotally connected between the piston rods38 of the hydraulic boom hoist cylinders 34 and the upper works 12 Theboom hoist cylinders 34 are connected to the upper works 12 at a pointpreferably near the lower end of the boom hoist cylinders 34, but may beconnected to the upper works 12 at any point along the bore 40 of theboom hoist cylinders 34. The boom 26 is connected to the piston rods 38of the hydraulic boom hoist cylinders 34 and the mast 36 by one or moreboom pendants 42. The boom pendants 42 may be connected to either themast 36 or the piston rods 38 of the hydraulic boom hoist cylinders 34,but preferably are connected at a point near the connection between themast 36 and the piston rods 38 of the hydraulic boom hoist cylinders 34.A boom backstop 44 is provided to prevent the boom 26 from exceeding asafe operating angle.

[0027] The position of the boom 26 is controlled by the hydraulic boomhoist cylinders 34. The mast 36 supports the connection between thehydraulic boom hoist cylinders 34 and the boom pendants 42 at a locationthat is distanced from the axis of the boom 26 to optimize the forces inthe boom pendants 42 and the hydraulic boom hoist cylinders 34. Thisarrangement also permits the hydraulic boom hoist cylinders 34 to imparta force having a component that is perpendicular to the axis of the boom26. This force is transferred to the end of the boom 26 by the boompendants 42.

[0028] Extending the hydraulic boom hoist cylinders 34 decreases theangle between the front of the boom 26 and the ground. Conversely,retracting the hydraulic boom hoist cylinders 34 increases the anglebetween the front of the boom 26 and the ground. Under normal operatingconditions, the hydraulic boom hoist cylinders 34 and the boom pendants42 are in tension from the weight of the boom 26 and any load beinglifted by the crane 10. Conversely, the mast 36 is in compression undernormal operating conditions.

[0029] As best seen in FIG. 2, the mast 36 and the hydraulic boom hoistcylinders 34 are pivotally connected to the top of the rotating bed 14of the upper works 12. The connection of the boom hoist cylinders 34 tothe rotating bed 14 is at a position that is behind and higher inelevation than the connection of the mast 36 to the rotating bed 14. Asbest seen in FIGS. 3-4, this configuration allows the hydraulic boomhoist cylinders 34 and the mast 36 to be lowered to an approximatelyhorizontal position on top of the upper works 12 when the crane 10 hasbeen disassembled for transport. It is important to minimize the overallheight of the disassembled crane 10 so that highway height restrictionswill not be violated during transport to and from the job site. Thisconfiguration also allows the hydraulic boom hoist cylinders 34 tocontrol the boom 26 even when the boom has been lowered to an anglewhich is below horizontal.

[0030] In the crane 10 of the preferred embodiment shown, two hydraulicboom hoist cylinders 34 are used in tandem. However, it should beunderstood that any number of hydraulic boom hoist cylinders 34,including a single hydraulic cylinder, can be used in the abovedescribed arrangement. The hydraulic boom hoist cylinders 34 must havesufficient capacity to function under the loads generated by theoperation of the crane 10 when lifting objects. The pistons 38 of thehydraulic boom hoist cylinders 34 should also have a stroke ofsufficient length so as to be lowered on top of the upper works 12 fordisassembly and transport without requiring disconnection from the mast36. In the preferred embodiment shown, which is for a crane having arating of 120-175 tons, each hydraulic boom hoist cylinder 34 has astroke of 160 inches.

[0031] In the preferred embodiment shown, the mast 36 is comprised of aframe. Alternatively, the mast 36 can be comprised of a pair ofindividual struts. The mast 36 should not interfere with the operationof the load hoist lines 46 or the boom backstop 44.

[0032] The upper works 12 further includes one or more load hoist lines46 for lifting loads. Each load hoist line 46 is reeved around a loadhoist line drum 48 supported on the rotating bed 14 of the upper works12. The load hoist line drums 48 are rotated to either pay out orretrieve the load hoist lines 46. The load hoist lines 46 pass through awire rope guide 50 attached to the upper interior side of the boom butt30 and are reeved around a plurality of boom top sheaves 52 located atthe upper end of the boom top 28. The wire rope guide 50 prevents theload hoist lines 46 from interfering with the lattice structure of theboom 26. A hook block 54 is typically attached to each load hoist line46.

[0033] As best seen in FIG. 2, the upper works 12 further includes apower plant 56, such as a diesel engine, enclosed by a power planthousing 58 and supported on a power plant base 60. The power plant base60 is connected to the rear of the rotating bed 14. Connected to thepower plant base 60 is a upper counter weight assembly 62 comprising aplurality of counter weights 64 supported on a counter weight tray 66.The power plant 56 supplies power for the various mechanical andhydraulic operations of the crane 10, including movement of the crawlers24, rotation of the rotating bed 14, rotation of the load hoist linedrums 48, and operation of the hydraulic boom hoist cylinders 34. Themechanical and hydraulic connections between the power plant 56 and theabove-listed components have been deleted for clarity. Operation of thevarious functions of the crane 10 are controlled from the operator's cab68.

[0034] As best seen in FIGS. 11 and 12, the wire rope guide 50 comprisesat least one positionable sheave 80. The positionable sheave 80 ismovable between a first position on the end of the boom butt 30 (seeFIG. 11) and a second position on the upper interior side of the boombutt 30 (see FIG. 12). As will be described in greater detail below inconnection with the preferred method of assembling the crane 10,locating the positionable sheave 80 in the first position on the end ofthe boom butt 30 allows a load hoist line 46 to be used for liftingobjects prior to assembling the boom top 28 and any boom inserts 32 tothe boom butt 30 of the crane 10. When in this position (as best seen inFIGS. 5-7), the wire rope guide 50 prevents the load hoist line 46 frominterfering with the lattice structure of the boom butt 30 by guidingthe load hoist line 46 around the end of the boom butt 30. The wire ropeguide 50 also minimizes eccentric loading of the boom butt 30 when usingthe load hoist line 46 to lift objects.

[0035] When the boom top 28 and any boom inserts 32 are assembled to thecrane 10, the positionable sheave 80 is located on the upper interiorside of the boom butt 30 (see FIG. 1). When in this position (see FIG.1), the wire rope guide 50 prevents the load hoist lines 46 frominterfering with the boom 26 by maintaining a separation between theload hoist lines 46 and the boom top 28 and any boom inserts 32irrespective of the boom angle

[0036] As best seen in FIGS. 11 and 12, the positionable sheave 80 issupported by a pivotal frame 82 pivotally connected to the boom butt 30at or near the interior edge 84 adjoining the upper interior side andthe end of the boom butt 30. The wire rope guide 50 of the preferredembodiment also comprises a stationary sheave 86 located on the upperinterior side of the boom butt 30. The stationary sheave 86 is supportedby a stationary frame 88 attached to the interior side of the boom butt30. The stationary frame 88 also supports the pivotal frame 82 when thepositionable sheave 80 is in the second position on the upper interiorside of the boom butt 30 (as shown in FIG. 12). When the positionablesheave 80 is in the first position on the end of the boom butt 30, thepivotal frame 82 is connected to the end of the boom butt 30 at or nearthe exterior edge 90 adjoining the upper exterior side and the end ofthe boom butt 30 (see FIG. 11).

[0037] An alternative embodiment of a positionable wire rope guide, alsocalled a load hoist line guide, is shown in FIGS. 17-20. As best seen inFIG. 17, the wire rope guide 300 of the alternative embodiment iscomprised of a first sheave 302 and a second sheave 304. The firstsheave 302 is supported by a first frame 306 and the second sheave 304is supported by a second frame 308. The first frame 306 is pivotallyconnected to one edge of the end of the boom butt 30. The first frame306 is also pivotally connected to the second frame 308. The secondframe 308 is removably connected to the opposite edge of the end of theboom butt 30 when the wire rope guide 300 is positioned on the end ofthe boom butt 30. In the alternative embodiment shown, a collapsiblestrut 310 is connected between the first frame 306 and the second frame308 to maintain rigidity between the first sheave 302 and the secondsheave 304 when the wire rope guide 300 is positioned on the end of theboom butt 30. A rigging platform 312 is also provided on the first frame306 (see FIG. 20).

[0038] The crane 10 of the preferred embodiment also comprises aself-handling system for assembling and disassembling the upper counterweight assembly 62. As best seen in FIG. 8, the upper counter weightassembly 62 self-handling system comprises a pair of counter weightpendants 110 connected to a counter weight pivot frame 114 by a pair oflinks 112. The function of these components will be discussed in greaterdetail below with respect to the procedure for self-assembly the crane10 of the preferred embodiment. However, these components are also usedas a boom 26 parking device. As shown in FIG. 16, the angle of the boom26 can be secured while the crane 10 is not in use by connecting thecounter weight pendants 110 to the links 112. The links 112 and thecounter weight pivot frame 114 are both connected to the upper counterweight assembly 62, which in turn is connected to the power plant base60. These connections are discussed in greater detail below with respectto the procedure for self-assembly the crane 10 of the preferredembodiment. Once the counter weight pendants 110 are connected, thepressure in the hydraulic boom hoist cylinders 34 can be released topermit the weight of the boom 26 to be carried by the upper counterweight assembly 62 and the power plant 56, thereby eliminating the needto maintain a constant pressure in the hydraulic boom hoist cylinders 34to maintain the angle of the boom.

[0039] The preferred method of self-assembling the boom hoist cylindercrawler crane 10 is best seen by referring to FIGS. 3-15 and thedescription above.

[0040] Referring to FIG. 3, the disassembled boom hoist cylinder crawlercrane 10 is delivered to the job site on a transport trailer 100.Additional components, such as the boom top 28, any boom inserts 32, thecrawlers 24, the car body counter weights 22, and the upper counterweight assembly 62, are delivered on separate transport trailers (notshown) prior to their assembly to the crane 10.

[0041] Referring to FIGS. 3-4, the pistons 38 of the hydraulic boomhoist cylinders 34 are retracted to raise the hydraulic boom hoistcylinders 34 and the mast 36 up off of the transport trailer 160. A boombutt pendant 102 is then connected between the end of the boom butt 30and the mast 36. In the preferred method of self-assembly, the wire ropeguide 50 is initially positioned on the end of the boom butt 30. One endof the boom butt pendant 102 is then connected to the mast 36 at a pointnear the connection between the mast 36 and the boom hoist cylinders 34.The other end of the boom butt pendant 102 is then connected to thepivotal frame 82 of the wire rope guide 50. When not in use, the boombutt pendant 102 remains connected to, and is stowed on, the mast 36.The hydraulic boom hoist cylinders 34 are then retracted an additionaldistance to raise the boom butt 30 off of the transport trailer 100(FIG. 4).

[0042] A plurality of jacking cylinders 104 attached to the car body 20are swung into a position straddling the transport trailer 100. Thejacking cylinders 104 are then extended to raise the car body 20 off ofthe transport trailer 100. The transport trailer 100 can then beremoved.

[0043] Referring to FIGS. 5-6, a load hoist line 46 is reeved around thestationary sheave 86 and the positionable sheave 80 of the wire ropeguide 50. A hook block 54 is rigged to the load hoist line 46. The endof the load hoist line 46 is connected to boom butt 30. The load hoistline 46 and the hydraulic boom hoist cylinders 34 are now used to removethe crawlers 24 from a transport trailer 100 and position them forattachment to the car body 20. The hook block 54 can be raised orlowered by rotating the load hoist line drum 48 to either pay out orretract the load hoist line 46. The angle of the boom butt 30 can bechanged by either extending or retracting the hydraulic boom hoistcylinders 34, thereby moving an object attached to the hook block 54further from or closer to the crane 10. The position of the upper works12 relative to the car body 20 is controlled through rotation of theswing bearing 18. Once a crawler 24 has been properly positioned, it isthen attached to the car body 20. A method and apparatus for assemblingthe crawlers 24 to the car body 20 are disclosed in U.S. Pat. No.5,427,256. Another method of assembling the crawlers 24 to the car body20 is disclosed in U.S. patent application Ser. No. 08/469,194.

[0044] After both crawlers 24 have been attached to the car body 20, thejacking cylinders 104 can then be retracted to lower the crane 10 ontothe ground. The jacking cylinders 104 are then stored against the sideof the car body 20. In the alternative, the jacking cylinders 104 can beremoved from the crane 10.

[0045] Referring to FIG. 7, the crane 10 may now be used to positionother crane components for assembly to the crane 10. For example, theload hoist line 46 and the hydraulic boom hoist cylinders 34 can be usedto position and assemble the car body counter weights 22 to the car body20.

[0046] The hydraulic boom hoist cylinders 34 are also used to assemblethe upper counter weight assembly 62 to the upper works 12. As best seenin FIG. 8, the crane 10 is used to lift the upper counter weightassembly 62 off of a transport trailer (not shown) and place it on theground behind the crane 10. A pair of counter weight pendants 110 arethen each attached to a link 112 connected to each side of the counterweight pivot frame 114. One end of each counter weight pendant 110 ispinned to the mast 36 at a point near the connection between thehydraulic boom hoist cylinder 34 and the mast 36. When not in use, thecounter weight pendants 110 remain connected to, and are stowed on, themast 36 (see FIG. 7).

[0047] The counter weight pivot frame 114 of the preferred embodiment iscomprised of a U-shaped frame having the legs of the “U” connectedbetween the power plant base 60 and the upper counter weight assembly62. The cross-member which is connected between the legs of the U-shapedframe provides rigidity to the structure. Alternatively, the counterweight pivot frame 114 is comprised of a pair of struts, one strut beingpivotally connected to each side of the power plant base 60.

[0048] As best seen in FIG. 8, the upper counter weight assembly 62 ofthe preferred embodiment comprises a plurality of counter weights 64supported on a counter weight tray 66. Attached to the interior of eachside of the counter weight tray 66 is a plurality of pendants 116.

[0049] In the preferred method of self-assembly, the crane 10 ismaneuvered to align the counter weight pivot frame 114 with the uppercounter weight assembly 62. The counter weight pivot frame 114 is thenpinned to the pendants 116 attached to the counter weight tray 66 (seeFIG. 8).

[0050] As best seen in FIG. 9, the hydraulic boom hoist cylinders 34 arethen extended to lift the upper counter weight assembly 62 off of theground. As the upper counter weight assembly 62 is lifted upwards by thehydraulic boom hoist cylinders 34, the counter weight pivot frame 114swings the upper counter weight assembly 62 through a vertical arc aboutthe axis of the connection of the counter weight pivot frame 114 to theupper works 12. The connection of the pendants 116 to the counter weightpivot frame 114 is forward of the center of gravity of the upper counterweight assembly 62 such that upper counter weight assembly 62 tiltstoward the rear of the crane 10 when suspended by the pivot frame 114.

[0051] As the upper counter weight assembly 62 is lifted into itsoperating position on the rear of the upper works 12, a roller 118engages the underside of the power plant base 60 (see FIG. 9A). As thehydraulic boom hoist cylinders 34 are extended further, the roller 118guides the upper counter weight assembly 62 forward until a hook 120 oneach side of the counter weight tray 66 engages a pin 122 on each sideof the power plant base 60. The reward tilt of the suspended uppercounter weight assembly 62 permits the hooks 120 to clear the pins 122during the lifting operation. Once the hooks 120 engage the pins 122,the hydraulic boom hoist cylinders 34 are extended further until apinning hole 124 located near the rear of each side of the counterweight tray 66 is aligned with an oval shaped hole 126 located on eachside of the power plant base 60 (see FIG. 9B). A limit switch (notshown) prevents the hydraulic boom hoist cylinders 34 from being overextended. A pin 128 is then placed through the each pinning hole 124 andoval shaped hole 126 to secure the upper counter weight assembly 62 tothe power plant base 60. Once the pins 128 are in place, the hydraulicboom hoist cylinders 34 are retracted to remove the tension in thecounter weight pendants 110 and the links 112. The counter weightpendants 110 are then disconnected from the links 112 and stowed on themast 36. Likewise, the links 112 are stowed on the power plant base 60.

[0052] In the preferred method of assembly, at least one of the car bodycounter weights 22 are assembled to the car body 20 prior to assemblingthe upper counter weight assembly 62 to the upper works 12 to addstability to the crane 10. Installation of the second car body counterweight 22 may interfere with the installation of the upper counterweight assembly 62 to the upper works 12. If only one of the car bodycounter weights 22 was installed prior to assembly of the upper counterweight assembly 62 to the upper works 12, then the second car bodycounter weight 22 should be installed at this stage of the craneself-assembly method.

[0053] Referring to FIGS. 11-12, the wire rope guide 50 is relocatedfrom a first position on the end of the boom butt 30 to a secondposition on the upper interior side of the boom butt 30. As best seen inFIG. 11, the hydraulic boom hoist cylinders 34 are extended to rest theboom butt 30 on the ground. Blocking 130 is placed under the exterioredge 90 of the boom butt 30 to prevent the ground from interfering withthe wire rope guide 50. The hook block 54 and the load hoist line 46 arethen derigged and removed from the wire rope guide 50. A pin 132 whichconnects the pivotal frame 82 to the exterior edge 90 of the boom buttis then removed. The hydraulic boom hoist cylinders 34 are thenretracted to raise the pivotal frame 82 in an upward arc about thepivotal connection of the pivotal frame 82 to interior edge 84 of theboom butt 30. As shown in FIG. 12, the pivotal frame 82 is positionedadjacent to the stationary frame 88. The pivotal frame 82 is thenconnected to the stationary frame 88 by installing a pin 134 throughholes in the pivotal frame 82 and the stationary frame 88.

[0054] The alternative embodiment of the positionable wire rope guide300 shown in FIGS. 17-20 is relocated through a similar procedure. Asshown in FIGS. 17-18, pin 314 is removed from the collapsible strut 310to allow the strut 310 to fold. Pin 316 is then removed to release theconnection between the second frame 308 and the end of the boom butt 30.The hydraulic boom hoist cylinders 34 are then extended to allow thefirst frame 306 to swing downwardly against the stop 318.

[0055] Referring to FIGS. 17-18, the boom butt pendant 102 isdisconnected from the first frame 306 and reconnected to a lifting link320 on the second frame 308. A lifting link pin 322, which secures thelifting link 320 when not in use, is removed to allow the lifting link320 to pivot with the boom butt pendant 102. The hydraulic boom hoistcylinders 34 are then retracted to draw the second frame 308 upwardstowards the first frame 306 by swinging the second frame 308 about thepivotable connection between the first frame 306 and the second frame308. The collapsible strut 310 is simultaneously folded as the secondframe 308 is raised.

[0056] Referring to FIG. 19, the second frame 308 is raised to aposition next to the first frame 306. Pin 324 is then installed torigidly connect the second frame 308 to the first frame 306. Thehydraulic boom hoist cylinders 34 are further retracted to swing thewire rope guide 300 upwardly until it flips over center.

[0057] Referring to FIG. 20, the wire rope guide 300 is then lowered onto the upper interior side of the boom butt 30 by extending thehydraulic boom hoist cylinders 34. Pin 326 is then installed to rigidlyconnect the first frame 306 of the wire rope guide 300 to the upperinterior side of the boom butt 30. The rigging platform 312 is thenlowered into position.

[0058] Referring to FIG. 13, the boom top 28 and any boom inserts 32 areassembled together on the ground adjacent to the boom butt 30. Blocking130 is typically used to support the boom top 28 and the boom inserts 32during the assembly process. The assembled boom top 28 and boom inserts32 are then connected to the interior edge 84 of the end of the boombutt 30. The connections between the boom butt 30, the boom top 28, andany boom inserts 32 can be one or more of the connections shown in U.S.Pat. No. 5,199,586.

[0059] Referring to FIG. 14, the hydraulic boom hoist cylinders 34 areretracted to lift the boom 26 to align the axis of the boom butt 30 withthe axis of the assembled boom top 28 and any boom inserts 32. Theexterior edge 90 of the end of the boom butt 30 is then connected to theassembled boom top 28 and any boom inserts 32 to complete the assemblyof the boom 26.

[0060] Referring to FIG. 15, the boom butt pendant 102 is disconnectedand preferably stowed on the mast 36. The boom pendants 42 are thenconnected between the mast 36 and the boom top 28. The load hoist lines46 are then passed through the wire rope guide 50 and reeved around theboom top sheaves 52. Finally, one or more hook blocks 54 are rigged tothe load hoist lines 46 (as seen in FIG. 1).

[0061] Self-disassembly of the crane 10 is accomplished by following themethod described above in reverse order.

[0062] Normally, double-acting cylinders like cylinders 34 are poweredby open loop pumps, because the rod end of the cylinder takes less fluidto move the piston than is displaced out of the piston end of thecylinder. Open loop pumps draw hydraulic fluid from a reservoir andfluid is returned from the cylinder to the reservoir. The volumedifferential between the rod end and the piston end of the cylinder canthus be easily accommodated.

[0063] However, open loop pumps are not as power efficient as closedloop pumps, and turn much slower, delivering lower flow rates, thancomparable closed loop pumps. Also, comparable horsepower open looppumps are more expensive than closed loop pumps. Larger displacementopen loop pumps generally require super charging the inlet either bypressurizing the reservoir or with a secondary pump. The super chargingpump must have the same flow rate as the main open loop pump. Because ofthese drawbacks, a unique hydraulic circuit using a closed loop pump wasdeveloped for crane 10. The hydraulic circuit is shown in FIG. 21. Asexplained above, the hydraulic cylinders 34 are preferably double-actingcylinders and are used during normal crane operations to control theboom angle, and during crane set up operations, particularly wheninstalling the upper counterweight assembly 62. When used to control theboom angle during normal lifting operations, the cylinders 34 aregenerally in tension. During the counterweight positioning operation,the cylinders 34 are in compression. As a result, the cylinders aresometimes controlled to move in a direction that is natural for them tofollow under the loads then being imposed. In this situation, the pumpis handling an overhauling load. That is, the pump is motoring, ordriving the diesel engine typically used to drive the pump In thepreferred circuit, the pump is subject to overhauling loads sometimeswhen the cylinders are extending and sometimes when the cylinders areretracting.

[0064] The major components of the circuit include the closed loop pump201, the double-acting cylinders 34, a charge pump 203, an auxiliarypump 205, also referred to as an accessories pump because it is alsoused to power auxiliary hydraulic accessories, a cylinder directionalcontrol valve assembly represented by dotted line 225, and areplenish-hot oil manifold, represented by dotted line 206, whichincorporates a relief valve 227 and a hot oil shuttle valve 229. Thepreferred directional control valve assembly 225 includes two solenoidcontrolled, spring biased two position valves 272 and 274. The preferredreplenish hot oil manifold 206 contains a hot oil shuttle valve 229,preferably Model No. DSGH-XHN, a relief valve 227, preferably Model No.RPGC-LNN, and two check valves 241 and 242, preferably Model No.CXFA-XAN, all in the form of cartridges that screw into the manifold.The cartridges are from Sun Hydraulics.

[0065] The closed loop pump 201 and charge pump 203, and the othercomponents within dotted line 208, are preferably all built-incomponents on a commercially available variable displacement pump, suchas the Series 90 pump from Sauer Sundstrand Corporation, Model No. 90 L100 KA 2 C 853 Fl E 33 6BA 20 42 24. This pump incorporates a swashplateas a directional flow controller so that either of the two ports 202 and204 of the pump 201 can be alternatively used as the discharge andintake ports. Alternatively, a closed loop pump with unidirectional flowcould be coupled to a separate directional flow controller tointerchangeably provide power to both sides of the cylinders 34. Thepreferred closed loop pump includes internal safety relief valves andother features which are not shown in FIG. 21 because they areconventional and form no part of the present invention.

[0066] The cylinders 34 are preferably identical. As a result, the samereference numbers are used to refer to the same parts of the cylinders34. Each cylinder 34 has a bore 236 and a piston 237 mounted in the bore236, forming a piston end 238 of the cylinder 34. A rod 38 is connectedto the piston 237 opposite the piston end 238. The rod 38 extends out ofan exit end of the bore 236 but is sealed at the exit end, forming a rodend 240 of the cylinder. A first passageway 218 is in fluidcommunication with the piston end 238, and a second passageway 216 is influid communication with the rod end 240 of the cylinder 34.

[0067] When the boom 26 is raised, the cylinders 34 are retracted. Theclosed loop variable displacement pump 201 is brought on stroke topressurize lines 211, 212, 213 and 214. Fluid is allowed to enterpassageway 216 into the rod end 240 of each cylinder 34 through checkvalves 224. The boom hoist directional control valve assembly 225 iselectrically actuated to the boom up position in which flow from thecharge pump 203 in lines 210, 215 and 276 passes through the valve 272and out lines 265 and 266 to the pilot operated valves 221 mounted oneach cylinder 34. The pilot signal opens the pilot operated valves 221,allowing hydraulic fluid to pass out of the cylinder bores 236 throughpassageways 218 Lines 234, 232 and 231 return the fluid to port 202 ofpump 201.

[0068] As the circuit is designed with a closed loop variabledisplacement pump, the flow in the lines into and out of the cylinders34 must be equal at the pump 201. It would be best if the ratio of thechange in volume of the rod end to the change in volume of the pistonend as the rod is extended or retracted is between about 1:2 and about1:1.1. In the presently preferred embodiment of the crane 10, the rod 38has a diameter of 5.5 inches and a cross sectional area of 23.8 squareinches. The bore 236 has a diameter of 12 inches, and a cross sectionalarea of 113.1 square inches. The preferred ratio of the change in volumeof the rod end 240 to the change in volume of the piston end 238 is thus(113.1-23 8): 113.1, or 1:1.27. Thus, for one gallon of hydraulic fluidforced into passageway 216, 1.27 gallons of hydraulic fluid comes outpassageway 218. The extra 0.27 gallons is drained from the circuitthrough the replenish-hot oil manifold 206, out line 259 to thehydraulic reservoir, leaving one gallon to return to port 202 of pump201 through line 23 1. The excess fluid is allowed out through line 233in the replenish hot oil manifold 206. The shuttle valve 229 is actuatedby the pressure in line 213 so that line 233 is connected to line 255.The fluid then passes through line 257 and relief valve 227.

[0069] When the operator wants the boom 26 to go down, the pump 201 isbrought on stroke far enough to once again pressurize lines 211, 212 and214 to a level sufficient to support the load. The boom hoistdirectional valve assembly 225 is electrically actuated to the boom down(extend) position in which flow from the charge pump 203 passes throughlines 210, 215 and 278, then through the valve 274, and out lines 263and 264 to the pilot operated valves 223 mounted on each cylinder. Thepilot signal opens the pilot operated valves 223, allowing hydraulicfluid to pass out of the rod end 240 of the cylinders 34 throughpassageways 216. At this time, the flow direction of the pump 201 isreversed, and port 202 becomes the discharge port of pump 201. Flowpasses through lines 231 and 234, check valve 222, and passageway 218,causing the rod 38 to extend. However, because the cylinder 34 is undertension, intake port 204 and lines 211 and 214 remain under highpressure.

[0070] As before, the flow into and out of each cylinder 34 must beequal at the variable displacement pump 201. However, in the boom downmode, one gallon of fluid from the rod end 240 of the cylinder 34results in a need for 1.27 gallons to enter the piston end 238. The 0.27gallons is made up from flow from the accessories pump 205 through thelines 251, 253 and 254 into the replenish-hot oil manifold 206, which ispositioned such that flow can enter line 233 from line 255 and join withthe flow in line 231 to line 232, 234 and enter piston end 238. Sincethe cylinder 34 is generally in tension during the boom-down operation,the lines 231, 232 and 233 are on the low pressure side of the pump 201.Hence, the make up fluid is being supplied from the accessories pump 205to the low pressure side of the hydraulic circuit.

[0071] At very steep boom angles, the cylinders 34 may be incompression. The hydraulic circuit of FIG. 21 allows for the closed looppump to handle extension under compressive loads as well, because asdiscussed above the preferred crane 10 also uses the cylinders 34 forcounterweight positioning operations.

[0072] During counterweight positioning operations, the cylinders 34 arein compression When the operator commands the cylinders to extend, lines231, 232, 233 and 234 become the high pressure side of the circuit,feeding the piston end 238 of the cylinders 34 through check valve 222.Port 202 becomes the discharge and high pressure port on the closed looppump 201. The boom hoist directional control valve assembly 225 isactuated so that pressure from the charge pump 203 can flow through line215, valve 274, and lines 263 and 264 to open pilot operated valves 223,allowing fluid to exit passageways 216. In the extend mode, additionalmake up flow from the accessories pump 205 is brought through lines 251,253 and 254 into the replenish-hot oil manifold 206. The pressure inline 233 causes the pilot line to operate valve 229 so that fluid mayflow from line 255 into line 213 and then to join with the flow in lines212 and 211 back to pump 201 through port 204 on the pump. Once again,the make up fluid supplied by the accessories pump 205 is fed into thelow pressure side of the hydraulic circuit.

[0073] When the operator commands the cylinders to retract during acounterweight positioning operation, lines 231, 232, 233 and 234 remainthe high pressure side of the circuit. Pump 201 is brought on stroke farenough to once again pressurize these lines to a level sufficient tosupport the load. The boom hoist directional control valve assembly 225is electrically actuated to the retract position so that flow from thecharge pump 203 in line 215 passes through valve 272 and out lines 265and 266 to the pilot operated valves 221 mounted on each cylinder 34.The pilot signal opens the pilot operated valves 221, allowing hydraulicfluid to pass out of the piston end 238 of the cylinders 34. At thistime, the flow direction of the pump 201 is reversed so that the rod 38begins to retract. However, lines 231, 232, 233 and 234 remain the highpressure lines since the cylinder 34 is under compression. Hence port202 is the intake port, but is still the high pressure port as well.Excess fluid from lines 212 and 214 passes out through line 213, valve229, lines 255 and 257, relief valve 227 and line 259 to the cooler andthen on to the reservoir.

[0074] The pilot operated valves 221 and 223 are mounted directly to thecylinders. In the event of a hose burst, pilot pressure is lost. Thepilot operated valves then close, holding the cylinder in place. Reliefvalves 226 and 228, on the other hand, allow excess pressure that coulddamage the cylinders (such as from thermal expansion when sunlight heatsup the cylinder) to escape.

[0075] The pilot operated valves 221 and 223 are identical, and arepreferably Model No. DKJS-XHN valve cartridges from Sun Hydraulics.These are what is known as pilot to open, two way valves with aninternal static drain. The relief valve 226 and the check valves 222 arepreferably both built into the same commercially available ModelSCIA-CCN cartridge from Sun Hydraulics. Relief valve 228 and check valve224 are likewise part of one cartridge. All four cartridges are screwedinto a single manifold mounted to the middle of the cylinder. Thismanifold is connected to the ends of the cylinder 34 by welded pipingthat is an integral part of cylinder 34. Relief valves 228 arepreferably set at 5000 psi, and relief valves 226 are preferably set at3000 psi. Any leakage from valves 228, 226, 223 and 221 is directed tothe low pressure reservoir, which is preferably a tank at atmosphericpressure.

[0076] The accessories pump 205 is preferably one of three sections of agear pump Model 323 9639 161 from Commercial Intertech of Youngstown,Ohio. Another section of this gear pump is the super charge pump thatsupplies charge pump 203. In crane 10, the accessories pump 205 is usedto power components on the lower works 16 through line 252, such asjacking cylinders 104, as well as to supply make-up fluid for the closedloop pump 201. Line 281 is a pressure pilot line from a power beyondport of a valve on the lower works. It is used to operate the piston ofpiston check valve 282 within the pump unload valve depicted by dottedline 280. The pump unload valve also includes an orifice 283 whichbleeds to tank. A relief valve 285 is in parallel with the piston checkvalve 282. The relief valve 285 allows for pressure relief when pump 205is running but fluid is not needed in line 252, but check valve 282 isnot open. Normally, flow through line 251 is directed through valve 282because the power beyond valve provides a signal through line 281 toopen piston check valve 282. The orifice 283 allows pressure to bleedout of line 281 so that check valve 282 can close when fluid is desiredto flow through line 252. A filter 270 cleans the fluid as it flows outof the pump unload valve 280 so that fluid entering the closed loopcircuit through replenish-hot oil manifold 206 is filtered. A checkvalve with substantial resistance 271 provides a parallel flow path tothe hot oil manifold 206 if filter 270 becomes blocked. Preferably afilter, not shown, is provided between the supercharger and the chargepump 203. The supercharger preferably provides hydraulic fluid at 75psi.

[0077] If the charge pump 203 were large enough, it could be used tosupply the make-up fluid needed for the cylinder differential throughcheck valves 207 and lines 217 or 219. However, in the preferred,commercially available variable displacement pump with built indirectional control 208, the built in charge pump 203 is not largeenough to perform that function, and thus the accessories pump 205 isused.

[0078] The preferred hot oil shuttle valve 229 has pressure pilot linesconnected to lines 213 and 233 to automatically operate the shuttlevalve. When the pressure in line 233 is higher than the pressure in line213, line 255 will be connected to line 213. On the other hand, when thepressure in line 213 is higher than the pressure in line 233, line 255will be connected to line 233.

[0079] Check valves 241 and 242 are included in the replenish hot oilmanifold 206 to take care of operating conditions in which the pressuredifferential between lines 213 and 233 is insufficient to open shuttlevalve 229. This is likely to occur at steep boom angles when thecylinder 34 are only in slight compression or tension. During thesesituations, make up fluid from line 255 can still enter the low pressureside of the circuit through check valve 241 or 242, depending on whetherline 258 or 256 has the lowest pressure. Check valves 241 and 242, whichhave a slight resistance, can also provide a parallel path for fluid toenter the closed loop part of the circuit. When the shuttle valve 229 isopen, it will have a small pressure drop across it as fluid starts toflow through it. When this pressure drop equals the slight pressureneeded to open the check valves 241 or 242, fluid will take both paths.Shuttle valve 229, however, provides the normal path by which fluidleaves the closed loop portion of the circuit since check valves 241 and242 only allow flow in one direction.

[0080] Relief valve 227 is preferably set to open at 350 psi. Thismaintains a minimum of 350 psi in the hydraulic circuit, which isimportant because when accessories pump 205 is running and no fluid isneeded for the accessories or as make-up fluid in the closed loop partof the cylinder circuit, the fluid from pump 205 will unload throughpump unload valve 280 and through lines 253, 254, 255 and 257. Reliefvalve 227 therefore maintains a minimum pressure for pump 205. Pilotoperated relief valve 209 similarly provides a minimum pressure andrelief for charge pump 203.

[0081] The hydraulic system is preferably controlled by a microprocessoras part of the overall crane control function. Examples of controlsystems for lift cranes using a microprocessor to control hydraulicfunctions are disclosed in U.S. Pat. Nos. 5,189,605; 5,297,019 and5,579,931, all of which are hereby incorporated by reference. As such,the crane 10 will preferably include transducers, such as transducers290, 292, 294 and 296, to monitor the fluid pressure at different pointsin the hydraulic system. Transducers 292 and 294 are used when thecylinders are in tension. If simple logic is used to control thehydraulic circuit when the cylinders are in compression, transducers 290and 296 may not be needed.

[0082] Instead of using two separate valves 272 and 274 in cylinderdirectional control valve assembly 225, a single four port, twosolenoid, three position valve such as Model No. 4WEJ6X/EG12N9Z45 valvefrom Mannesmann Rexroth could be used. In that case the valve wouldeither be in a closed position, preventing any movement of the cylinder,or in a boom up or boom down position In still a further alternative, atwo position, three way valve with only one solenoid could be used. Inthat case, the cylinders 34 would operate when the valve was actuated,and the movement direction of the cylinders would be controlled only bythe pump swash plate.

[0083] One of the benefits of using the two separate valves 272 and 274in directional control valve assembly 225 is that both valves can beopened simultaneously. One problem which was encountered when a singlevalve was used in an earlier design of the hydraulic circuit used oncrane 10 was that as loads were applied to the cylinders 34 with thevalves 221 and 223 closed (such as when the crane picks up a load, andthe tension in the rods is increased), the side of piston 237 which isunder increased pressure compresses slightly, allowing the piston 237 tomove and extra fluid to enter the opposite side of the cylinder throughcheck valve 222 or 224. When the load is removed, this fluid stays inthe cylinder, and the side of the cylinder with the extra fluid in itends up with a higher fluid pressure than the circuit pressure. When thevalve to that side of the cylinder is later opened, the extra fluidspurts out and the cylinder jerks.

[0084] By allowing both valves 272 and 274 to be operated independently,both valves 221 and 223 can be open, closed or one can be open while theother is closed. This gives more flexibility to the control of thecylinders 34. Also, the jerking problem can be avoided by leaving theappropriate valve open. For example, when the boom is in its properposition to lift a load, and the rods 38 are in tension, valve 272 canbe actuated, which will then open valves 221. Since the cylinders are intension and valves 223 are closed, the pistons 237 will not move.However, as a load is picked up by the crane, the pressure increases inrod end 240 of cylinders 34. As the fluid on that side compressesslightly, the piston moves and fluid enters piston end 238. When theload is released, the tension in rods 38 is returned to where it wasbefore the load was picked up, and the extra fluid that entered pistonend 238 of cylinders 34 can flow back out through open valve 221,avoiding the build up of extra pressure. Thus, all the time the crane islifting loads the valves 221 can be left open, and if the boom angleneeds to be changed, valves 223 are opened as described before. When thecylinders 34 are in compression, valves 223 can be left open to avoidthe same problem of extra fluid in the rod end 240 when the amount ofcompressive load is increased and then reduced.

[0085] In the preferred embodiment of the crane 10, the rod 38 is sizedso that it carries intended loads in compression. Since it is desirableto keep the diameter of the rod 38 to a minimum, and because thebuckling strength of a rod decreases as its effective length increases,the counterweight handling system is designed so that the rods 38 onlyhave to be operated with limited extension while the cylinders 34 are incompression. This reduces the potential buckling problem and allows therods 38 to be designed with smaller diameters than if the rods 38 couldbe fully extended in compression. The tensile strength of the materialused to make the rods 38 is high enough so that even at this smallerdiameter, the rods 38 have sufficient tensile strength to safely handlemaximum expected tension loads.

[0086] The preferred hydraulic circuit described above allows a closedloop pump to power the double-acting hydraulic cylinders 34. It alsoprovides that the extra fluid needed to make up for the cylinderdifferential is always added to the low pressure side of the circuit.Since the closed loop pump often handles overhauling loads, sometimesthe low pressure side of the circuit is connected to the discharge portof the closed loop pump. The preferred circuit takes this into account,and allows the make-up fluid to go to the pump when the intake port ison the low pressure side, or go to the cylinder when the pump intakeport is on the high pressure side. In this way the circuit can be usedto operate the double-acting cylinders in both a tension and compressionsituation. Further, the pump supplying the make-up fluid can be lessexpensive because it is always supplying to the low pressure side of thecircuit.

[0087] It should be appreciated that the apparatus and methods of thepresent invention are capable of being incorporated in the form of avariety of embodiments, only a few of which have been illustrated anddescribed above. The invention may be embodied in other forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive, and the scope of the invention is, therefore,indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

We claim:
 1. A hydraulic circuit comprising: a) a first double-acting hydraulic cylinder having a bore, a piston mounted in said bore and forming a piston end of said cylinder, and a rod connected to said piston opposite said piston end and extending out of an exit end of the bore but being sealed at the exit end of the bore, thus forming a rod end of said cylinder, the cylinder having a first passageway in communication with said piston end and a second passageway in communication with the said rod end; b) a closed loop hydraulic pump having, during operation, a low pressure port in fluid communication with a low pressure side of the hydraulic circuit and a high pressure port in fluid communication with a high pressure side of the hydraulic circuit; c) a directional flow controller and hydraulic lines connecting the closed loop pump and the double-acting cylinder such that fluid from the pump can be directed to either said first or second passageways and fluid from the other of said first or second passageways is directed to return to the pump; d) a second hydraulic pump in fluid communication with the closed loop hydraulic pump so as to supply make-up hydraulic fluid to the low pressure side of the hydraulic circuit when said rod is being extended; and e) a valve in fluid communication with the first passageway when the rod is being retracted to allow excess hydraulic fluid to flow out of the circuit.
 2. The hydraulic circuit of claim 1 wherein the directional flow controller is built into the closed loop pump such that the ports on the pump can be alternatively used as discharge and intake ports.
 3. The hydraulic circuit of claim 1 wherein the pump is a variable displacement pump.
 4. The hydraulic circuit of claim 1 further comprising a replenish manifold valve which connects said second pump to the low pressure side of the hydraulic circuit when the rod is being extended and connects the first passageway to the valve when the rod is being retracted.
 5. The hydraulic circuit of claim 1 wherein the valve is a pilot operated relief valve.
 6. The hydraulic circuit of claim 1 further comprising first and second pilot operated valves, the first pilot operated valve controlling flow of hydraulic fluid out of the first passageway and the second pilot operated valve controlling flow of hydraulic fluid out of the second passageway.
 7. The hydraulic circuit of claim 6 further comprising a cylinder directional control valve assembly connected to a charge pump which provides pressurized hydraulic fluid to operate the first and second pilot operated valves.
 8. The hydraulic circuit of claim 7 wherein the cylinder directional control valve assembly is electrically operated.
 9. The hydraulic circuit of claim 7 wherein the charge pump and the closed loop pump are built together and powered from a common drive shaft.
 10. The hydraulic circuit of claim 1 further comprising a second double-acting hydraulic cylinder having the same components and acting in parallel with said first double-acting cylinder.
 11. The hydraulic circuit of claim 1 wherein the excess hydraulic fluid from the valve flows to a low pressure reservoir.
 12. The hydraulic circuit of claim 7 wherein the charge pump is a different pump than the second hydraulic pump.
 13. A crane having an upper works rotatably mounted on a lower works and a boom pivotally mounted on the upper works comprising: a) a mast pivotally connected to the upper works, b) a double-acting hydraulic cylinder having a bore, a piston mounted in the bore and forming a piston end of said cylinder, and a rod connected to said piston opposite said piston end and extending out of an exit end of the bore but being sealed at the exit end of the bore, thus forming a rod end of said cylinder, the cylinder having a first passageway in communication with said piston end and a second passageway in communication with said rod end, one of the piston end of the cylinder and the rod being pivotally connected to the upper works and the other of the piston end of the cylinder and the rod being pivotally connected to the mast, c) a closed loop hydraulic pump having, during operation, a low pressure port in fluid communication with a low pressure side of the hydraulic circuit and a high pressure port in fluid communication with a high pressure side of the hydraulic circuit, and d) a directional flow controller and hydraulic lines connecting the closed loop pump and the double-acting cylinder such that fluid from the pump can be directed to either said first or second passageways and fluid from the other of said first or second passageways is then directed to return to the pump.
 14. The crane of claim 13 wherein the directional flow controller is built into the closed loop pump such that the ports on the pump can be alternatively used as the discharge and intake ports.
 15. The crane of claim 14 further comprising a second hydraulic pump in fluid communication with the closed loop hydraulic pump so as to supply make-up hydraulic fluid to the low pressure side of the hydraulic circuit when said rod is being extended and a relief valve in fluid communication with the first passageway when the rod is being retracted to allow excess hydraulic fluid to flow to a low pressure reservoir.
 16. The crane of claim 13 wherein the rod is pivotally connected to the mast and the piston end of the cylinder is pivotally connected to the upper works.
 17. The crane of claim 13 wherein the ratio of the change in volume of the rod end to the change in volume of the piston end as the rod is extended or retracted is between about 1:2 and about 1:1.1.
 18. The crane of claim 17 wherein said ratio is about 1:1.27.
 19. The crane of claim 15 wherein when the double acting cylinder is in tension and being extended, the make-up fluid is directed to the piston end of the cylinder.
 20. The crane of claim 15 wherein when the double acting cylinder is in compression and being extended, the make-up fluid is directed to an intake port of the closed loop pump.
 21. The crane of claim 13 wherein the hydraulic cylinder is in tension when the crane is lifting a load.
 22. The hydraulic circuit of claim 7 wherein the control valve assembly comprises two valves each having at least first and second positions which can be operated independently of each other. 